1. Field of the Invention
The present invention relates to a rectification feedback high frequency circuit arrangement for sharply cutting off transmission bands of each channel in repeated communications of sounds, data and the like through plural narrow-band channels allotted close to each other, and particularly, so as to immediately fix a suitable transmission band property adapted to the variation of operational conditions (e.g. temperature), each time the repeated communication is reopened.
2. Description of Related Art
For instance, in sound communications, data communications and the like of press-talk type, plural narrow-band channels close to each other are allotted thereto. As a result, it is required in each of the transmission channels to sharply cut off both sides of each of the transmission bands for to prevent mutual interference. Therefore, in the communication apparatus of this kind, the rectification feedback which facilitates the sharp cut off of both sides of the transmission bands is generally effected by feeding-back with an adequate gain an envelope signal obtained by the rectifying detection of a partly branched transmission output high frequency signal through a low pass filter having an adequate band characteristic, so as to attain a desired narrow band transmission property.
However, the utilization of communications of this kind is recently remarkably increased, and hence plural allotted transmission channels are entirely used in practice without any vacant channels. As a result, the interference between adjacent narrow band transmission channels through narrow guard-bands has caused practical troubles. Consequently, it is required for removing interference between adjacent channels to extremely increase the attenuation on both sides of the transmission bands by increasing the feedback rate of conventionally adopted rectification feedback.
However, in the case that the required narrow band transmission property can be attained by the rectification feedback at this high feedback rate, for instance, between an interval immediately after the reopening of intermittent transmission and a subsequent transmission interval, temperature, applied voltage and the like in each of the circuit elements are varied, even if slightly, and hence the transmission band characteristic, which has been attained by the rectification feedback at high rate, is varied thereby. As a result, transmission obstacles, (e.g. immediately after the opening of press-talk, the aforesaid interference between adjacent channels is caused) are increased. Consequently, the prevention of these communication obstacles, particularly, of adjacent channel interference caused by the variation of transmission band characteristic at the reopening of transmission has been a conventional problem to be solved.